We present evolutionary synthesis models of starbursts on top of old stellar populations to investigate in detailed time evolution the relation between Hα luminosity and star formation rate (SFR). The models show that several effects have an impact on the ratio between L(Hα) and SFR. Metallicity different from solar abundance, a time delay between star formation and maximum Hα-luminosity, and a...

We present empirical formulae for the electron density vs. line profile widths and shifts developed from precise measurements of hydrogen Balmer series alpha and beta emissions for diagnostics of laser-induced plasma. The formulae are for the Stark width and Stark red shift of the Hα line, as well as for the Stark width and peak separation of the Hβ line and are tested using measurements of Hα ...

This paper presents (Hα + [NII]) imaging and spectroscopy of a previously unknown, highly evolved planetary nebula of low excitation. It was discovered serendipitously from AAO/UKST Hα Survey images as part of a project to exploit the survey data and has evaded detection by previous surveys due to very low surface brightness. It is a remarkably annular planetary nebula, some 19 across, making i...

It is predicted that the Hα emission line at the early nebular epoch of type II-P supernovae may display robust observational effects of radiation damping wings. Monte Carlo simulations demonstrate that the Hα line with the optical depth typical of the early nebular epoch acquires extended wings and redshift and becomes broader compared to the Sobolev approximation case. The strength of these e...

We present simultaneous Hα, Na i D 1 , D 2 , and He i D 3 spectroscopic observations on the RS CVn system UX Ari. We have found a dramatic increase in the excess Hα emission equivalent width by a factor of 2 in an interval of 1 day that indicates the beginning of a strong flare in this system. The presence of the He i D 3 in emission in coincidence with the enhancement of the Hα emission confir...

We describe a technique to identify Be stars in open clusters using Strömgren b, y, and narrow-band Hα photometry. We first identify the B-type stars of the cluster using a theoretical isochrone fit to the (b−y, y) color-magnitude diagram. The strongest Be stars are easily identified in a (b−y, y−Hα) color-color diagram, but those with weaker Hα emission (classified as possible Be star detectio...

This document provides a brief summary estimate of Galactic free-free emission and Hα emission and their relationship. Particular emphasis is placed on estimating the potential freefree emission in the region of significant confusion for CMB anisotropy measurements. Existing x-ray, ultraviolet and Hα emission provide limits on the radio free-free emission and vice versa. These limits are genera...

In a search for new Galactic planetary nebulae from our systematic scans of the AngloAustralian Observatory/United Kingdom Schmidt Telescope (AAO/UKST) Hα survey of the Southern Galactic Plane, we have identified a Population I Wolf-Rayet star of type WN7h associated with an unusual ring nebula that has a fractured rim. We present imagery in Hα, the 843-MHz continuum from the Molonglo Observato...

Received ; accepted – 2 – ABSTRACT We find that a non-axisymmetric bow shock model, with an appropriate choice of parameters, could fit the line splitting velocity field of the cone-like Hα nebula in NGC 4945 better than a canonical cone model. Meanwhile, the bow shock model could also reproduce the morphology of the Hα nebula. The bow shock results from the interaction of the galactic superwin...

Using new radiative modelling capabilities in twodimensional (2D) cartesian geometry,we investigate the vertical variations of the Hα source function in filaments. It is shown how the two-dimensional geometry can affect the transfer of the Hα line into filaments and, consequently, how assumptions on the geometry of the model may influence a further interpretation of observations. A special atte...